1. Field of the Invention
This invention relates to a novel ceramic article, a carrier for a catalyst, methods for the production thereof, a catalyst for producing ethylene oxide using the carrier, and method for producing ethylene oxide. Particularly, it relates to a ceramic article calcined at elevated temperatures and endowed with acid points, a carrier for use in a catalyst, methods for the production thereof, a catalyst for producing ethylene oxide using the carrier, and method for producing ethylene oxide. More particularly, it relates to a ceramic article containing aluminum, silicon, and titanium and manifesting strong acid points in consequence of the calcining at 1,000°-2,000° C., a carrier for use in a catalyst, methods for the production thereof, and method for producing ethylene oxide.
2. Description of the Prior Art
The ceramic articles using the oxides of aluminum, silicon, titanium, etc. as basic materials generally possess exceptionally excellent thermal, mechanical, electrical, and chemical properties and find utility in applications too many to enumerate. Those of the ceramic articles which excel in thermal and mechanical strength are extensively utilized in the field of chemical industry as a carrier for a catalyst and as a refining material and in the field of bioceramics as artificial bones and artificial teeth which are required to possess affinity for living organism. Those of the ceramic articles which possess chemical properties are used for analysis utilizing the adsorbing desorbing property of a chemical substance and particularly those of the ceramic articles which possess acid points are utilized by themselves as a catalyst for the oxidation of olefins and the dehydrogenation of hydrated compounds.
JP-A-54-32,408, for example, discloses a non-acidic filler containing alumina, silica, and titania in a total amount of not less than 99% by weight, containing metals of the groups Va, VIa, VIIa, VIII, Ib, and IIb in the Periodic Table of the Elements in a total amount of less than 0.1% by eight as reduced to metal oxides, and assuming no acidic color in methyl red having a pKa of +4.8.
Further, JP-A-55-145,677 discloses a method for the production of ethylene oxide characterized by using a silver catalyst formed by using the non- acidic filler mentioned above as a catalyst carrier and depositing thereon silver and, when necessary, further an alkali metal component or an alkaline earth metal component. U.S. Pat. No. 4,812,437 discloses a carrier composed mainly of α-alumina and having a specific surface area, water absorption ratio, average pore diameter, silica content and sodium content and assuming acidic color in an indicator having pKa of +4.8.
JP-A-62-4,444 discloses that a carrier having small amount of impurities is obtained by mixing an aluminum compound with a salt of a metal of the group IA in the Periodic Table of the Elements and calcining it, and the catalyst using the carrier is excellent in stability. JP-A-4-363,139 discloses a carrier which contains an element of 4-6 Cycles of the groups IIIa-VIIa and IIIb-Vb in the Periodic Table of the Elements in α-alumina and the catalyst using such carrier gives high selectivity and long life. Further, U.S. Pat. No. 5,100,859 discloses a carrier comprising a high purity α-alumina, an alkali earth metal oxide, a silicon oxide and zirconium oxide, and the catalyst using such catalyst gives a high initial selectivity and long life.
On the other hand, a carrier for a catalyst provided on the surface of α-alumina with a coating layer of amorphous silica and used for the production of ethylene oxide (U.S. Pat. No. 5,077,256) and a carrier for a catalyst provided on the surface of α-alumina with a coating layer of amorphous silica-alumina and used for the production of ethylene oxide (U.S. Pat. No. 5,395,812) have been known to the art. These patent publications, however, neither suggest anything about a ceramic article containing aluminum, silicon, and titanium and manifesting acidity nor propose anything about a method for the production of the ceramic article.
Generally, ceramic articles possessing acid points are used as a dynamic blade and static blade of a gas turbine and a combustion chamber of a reciproengine as a construction material, for spraying on a turbine blade or a corn as a thermal isulation material and for a thermal absorption material utilizing the acidity thereof, but as a chemical use there are used as catalysts or carriers for use in catalysts which are useful for various oxidation reactions, reduction reactions, addition reactions, and decomposition reactions. They are required to possess high thermal stability in any of these applications and they derive huge economic effects from the high thermal stability. It is predicted that a high-temperature heat treatment will suffice to impart high thermal stability and mechanical strength to such carriers. It is also the fact that the heat treatment performed at a high temperature deprives the such carriers of acid points.
An object of this invention, therefore, is to provide a novel ceramic article, a carrier for a catalyst, methods for the production thereof, a catalyst for producing ethylene oxide using the carrier, and method for producing ethylene oxide.
Another object of this invention is to provide a ceramic article calcined at a high temperature and endowed with high thermal stability and acid points, a carrier for a catalyst, method for the production thereof, a catalyst for producing ethylene oxide using the carrier, and method for producing ethylene oxide.
Still another object of this invention is to provide a catalyst for producing ethylene oxide excellent in a catalyst performance, i.e., activity, selectivity and life, and a method for producing ethylene oxide using such catalyst.